1968 Volume 41 Issue 5 Pages 1068-1073
The charge-transfer (CT) bands of complexes of alkylsubstituted pyrroles and chloranil or tetracyanoethylene (TCNE) were found to consist of two closely situated peaks. The peaks were assigned to transitions originated from the highest occupied, and second-highest occupied orbitals of the donor. The energy of the CT absorption band is hardly affected even by the presence of a bulky substituent such as a t-butyl group at the pyrrole nitrogen. Hence, the acceptor molecules were thought not to be close to the 1-position of the pyrryl group. In the case of 1-phenylpyrrole, the first CT bands are at almost the same positions as those of the corresponding complexes of 1-methylpyrrole. The bands show red shifts if methyl groups are introduced either on the pyrryl group or on the phenyl group, so that the planes of the two groups are twisted around the N–C bond between them. Thus the acceptor molecules were concluded to interact mainly with the pyrryl group.
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